Screw propeller and similar appliance



May 15, 1923.

1,454,967 J. H. w; GILL SCREW PROPELLER AND SIMILAR APPLIANCE Filed'June 15 1920 v UNITED SATEd rarest orrrcs.

JAMES HERBERT WAINWRIGHT GILL, F NORFOLK, ENGLAND, ASSIGNOR T0 GILLPROPELLER COMPANY LIMITED, 0]? KINGS LYNN, ENGLAND, A COMPANY OF GREATBRITAIN.

s'cnnw PROPELLEB AND SIMILAR APPLIANCE.

Application filed June 15 1920. Serial No. 389,195.

To all whom it may concern:

Be it known that I, JAMES HERBERT WAINWRIGHT GILL, a subject of the Kingof England, and residing at Norfolk, in England, have invented certainnew and useful Improvements in Screw Propellers and Similar Appliances,of which the following is a specification.

This invention relates to screw propellers 10 and similar appliances ofthe axial flow type such as are employed to impart energy to fluidstreams or to develop propulsive reaction.

According to this invention the blades of the propeller are disposedwithin and carry 'on them a curved shroud whose inner surface has acontour'which is substantially that of a nozzle designed to give regularprogressive increase in velocity or head to the fluid in which thepropeller rotates. The pitch of the blades increases in the direction offlow through the shroud the pitch hav ing a definite relationship to theshape of the shroud to conform to the acceleration of the fluid streampassing through the shroud. The blades are carried on a suitably shapedhub which may conveniently be cylindrical though in some cases shapedotherwise and the shroud is formed integral with or is attached to theendsof the blades so that these are positioned within the shroudpreferably otherwise than at the centre of the length of the latter andnearer to the larger end. The, axial length of the shroud is such thatis less than the diameter of the propeller and greater than the axiallyprojected width of the blades while the contour of the inner surface ofthe shroud is, as mentioned, substanatially that of a nozzle of.particular design. The object of the invention is to reduce interferencewith the natural contraction of the fluid stream under the increasingvelocity impressed thereon and also to minimize discontinuity of flowand its contingent effects. These objects are attained by controllingvelocities and pressures in the fluid stream during its forcedacceleration,

The design of the nozzle-shaped'shroud should be such as to assist inthe formation of vortex action resembling that of a free spiral vortexand thus tominimize dissipation of energy in the fluid which is directlyacted upon by thepropeller. Inthe case of a fluid such as water the areaof the stream which is acted upon by the propeller contracts under theincreasing velocity and this natural contraction is assisted andcontrolled by the vortex shaped shrouding ring. True cavitation dependson the stream velocity at which the fluid acted upon will follow up thepropeller blades, and whilethere is a limit to this velocity, incipientcavitation, which is largely due to radial flow and local eddies, andtends to occur at velocities of flow below the above mentioned limit,can be practically eliminated by means of a shrouding ring shaped asdescribed.

The present invention has various advantages when compared with otherknown types of propeller more particularly when the invention is appliedto ship propulsion. By promoting steady flow and preventing cavitiesfrom collapsing in contact with the blades and boss of the'propelle'rthe improved construction reduces the erosive effect consequent oncavitation.

The employment of the nozzle shrouding ring strengthens the propellerand permits of higher speeds of revolution While minimizing vibration.Eddy losses and radial flow are reduced as also is the out ofpitch?effect which occurs with ordinary propellers when mounted on inclinedshafts. Further the effect of threshing which occurs when a vesselpitches is lessened and the shrouding ring also obviates fouling of thepropeller by ropes or nets. When employed for going astern a propellerprovided with the improved shroud'acts as an ordinarypropeller but as ifit was of less diameter and thus it affords an advantage as comparedwith a turbine propeller fitted with guide vanes. 1

The accompanying drawings illustrate by way'of example one constructionof prothe, blades A is mounted a nozzle-shaped shroud C which is eitherformed integral with the blades or separate and attached thereto in somesuitable manner. The blades A preferably have a gaining pitch so as 'toconform with the acceleration of the water passing through the shroud C.i The length of the shroud C may vary in v accordance with requirementsand the conditions under which the propeller is to be used. In theconstruction shown the length of the nozzle measured in the axialdirection is about three-quarters of the smaller diameter ofthepropeller. The smaller and outlet end .6 has a diameter which isabout .8 of the small diameter of the propeller. It will be noted thatthe blades A are not positioned at the centre of the shroud C but to oneside of this centre and somewhat towards the larger end C of the shroud.

In some cases the hub B may be split and handed to allow for uniformcontraction of the shroud-C where the latter is made in- I tegral withthe blades.

The leading edge C atthe inlet end of the shroud may be enlarged with anoutside bulb while the after edge C is fined off from the inside, butifthe propeller is likely to encounter ice or other obstructions throughwhich it is desirable to cut the edge C may be serrated.

The contour of the shroud C approximates to that of a portion of a freespiral vortex and this conforms to the path which is naturally followedby the water acted on by the propeller blades. The pitch of the bladesincreases in the direction of flow through the shroud to conform-to theacceleration of-ithe Water passing through the shroud and bears adefinite relationship to the shape of the shroud. When a propeller thusformed and shrouded is operating against; a dead pull, as in towing, theradial effect and eddy losses are reduced and the propeller operatesefficiently as an axial flow pump. The propeller will act .eflicientlywhen going astern but it then functions as an ordinary propeller of lessdiameter.

What I claim as my invention and desire to secure by Letters Patentis 1. In a screw propeller the combination of a hub, blades radiatingfrom the hub, and a shroud mounted on the ends of the blades, the innersurface of the shroud having approximately the contour of a nozzledesigned to give regular progressive increasein velocity or head to thefluid stream on which the propeller operates, and the blades havingaxial increase of pitch in the direction of flow through the shroud toconform with the acceleration of the water passing through the shroud.

2. In a screw propeller the combination of i a hub, blades radiatingfrom the hub, and a shroud mounted on the ends of the blades, the innersurface of the shroud having ap proximately the contour of a nozzledesigned to give regular vprogressive increase in velocity or head tothe fluid stream on which the propeller operates, the length of theshroud in the axial direction being less than the diameter of thepropeller but greater than the axially projected width of the propellerblades, the blades having axial increase of pitch in the direction offlow through the shroud to conform with the acceleration of the waterpassing through the shroud. 3. In a screw propeller the combination of ahub, blades radiating from the hub, and a shroud mounted on the ends ofthe blades, the inner surface of the shroud having approximately thecontour of a nozzle designed to give regular progressive increase invelocity or head to the fluid stream on which the propeller operates,and the blades being positioned intermediate theends of the shroud butotherwise'than at the center of its length, the blades having axialincrease of pitch in the direction of flow through the shroud to conformwith the acceleration of the water passing through the shroud.

i. In a screw propeller the combination of a hub, blades radiating fromthe hub, and a shroud mounted on the ends of the blades, said shroudhavinga length which measured in the axial direction is less than thediameter of the propeller but is greater than the axially projectedwidth of the blades, thethe shroud being curved to an approximatelyconical form and being outwardly flared toward one end, the blades beingpositioned within the shroud intermediate the ends of 5 the latter butotherwise than at the center of its length and said blades having axialincrease of pitch in the direction of flow through the shroud to conformwith the acceleration of the water passing through the shroud. 10 Intestimony whereof I have signed my name to this specification.

JAMES HERBERT WAINWRIGHT GILL.

